Gear forging



Oct. 17, 1967 R. c. CLERK 3,347,082

GEAR FORGING Filed Aug. 14, 1964 2 Sheets-Sheet 1 INVEN T08 20.5287" 6'. C1. E

R. C. CLERK Oct. 17, 1967 GEAR FORGING 2 Sheets-Sheet 2 Filed Aug. 14, 1964 I/WEA To R 92M816, C4 HM United States Patent 3,347,082 GEAR FORGING Robert C. Clerk, Maidenhead, England, assignor to Clerk, King, Poynter & Co. Ltd., Reading, England Filed Aug. 14, 1964, Ser. No. 389,545 Claims. (Cl. 72-362) The object of the present invention is to provide a means of producing gear blanks the periphery of which is forged substantially to an involute tooth for the desired number of teeth ready for finishing and/ or heat treatment in the accepted manner.

The purpose of the invention is not only to save the time and cost involved in rough bobbing a circular blank, not only to reduce the material cost of the blank and minimise swarf disposal, but more importantly to reform the periphery of the blank so that the grain of the metal follows the tooth form and is rendered very much denser at the roots in consequence, in contradistinction to the established methods of gear cutting wluch sever the tangential grain flow of the blank so that the gear teeth tend to be weak at the important root boundaries.

It is well known that this can be partially achieved by axial traverse rolling or die stamping which induces considerable axial bias in the grain flow whilst reforming the blank periphery thereby increasing the strain on application of load. It can also be achieved by circumferential rack rolling which however due to the necessity for consecutive impressioning imparts a slight ripple to the grain flow, and is in any case economic only for large volume production.

According to the present invention we provide a method of forming gear teeth upon metal blanks which comprises subjecting the blank to a simultaneous forging operation by a number (equal to the number of teeth to be formed) of radially disposed tooth ended punches attached to inertia masses to which is applied a penetration velocity high enough to induce radial outwards lift or splash of the deformed metal from the tooth roots.

The method of the invention when applied to hot forming allows for immediate withdrawal of the involute punches at the limit of penetration or of each partial penetration, but for cold working the punch tips may be left substantially in contact with the partial penetration with enough clearance only for renewal of the lubricant film between punches and work.

A machine for performing the method of the invention comp-rises essentially means to support the gear blank, a multiplicity of tooth ended and radially guided punches and means for simultaneously applying to all of the punches and inertia masses attached thereto a high speed, high momentum inwards movement to hammer the rim of the supported blank.

These and other features of the invention are embodied in a preferred form of gear forming machine which will now be described by way of example with reference to the accompanying drawings in which:

FIGURE 1 is a vertical axial section through the machine.

FIGURE 2 is a horizontal section on IIII of FIG- URE 1..

The preferred form of gear forming machine comprises: A work holder 1 to accept and locate the blank 2 to be forged with the axis of the blank vertical. A plurality of radial inwards involute punches 3 equal to the number of teeth to be formed on the blank 2. An annular guide ring 4 has bushed radial holes 5 in which punch mandrels 6 are located and enabled to slide radially. A plurality of inertia masses 7 are attached to the ends of the punch mandrels 6. A pluarlity of suspension links 8 and springs 9 transfer a proportion (say half) of the weight of the overhung inertia masses to, and compensate for vertical tolerances in, a plurality of actuating levers 10 intermediately lengthwise each of which is pivoted an actuating link 11. A double acting air cylinder 12, centred in relation with the work holder 1, supports a plurality of tangential pivots 13 radiating from the cylinder for attachment of the actuating levers 10 and a like plurality of tangential pivots 14 radiate from the piston rod 15 for attachment of the actuating links 11. A single acing cylinder 16 is associated with the said double-acting cylinder 12 and with the centring guide ring 4 to provide a floating support for the weight of the double-acting cylinder 12, of the actuating levers 10 and links 11, and of that part of the weight of the inertia masses 7 supported through the action of the suspension links 8 and springs 9.

The effect of the springs 9 acting on the suspension links 8 through lever 17 (each lever 17 and link 8 acting as a bell crank pivoted at pin 18) is to urge the pins 19 connecting the suspension links 8 and actuating levers 10 downwardly, and since no such movement is possible, this results in considerable portion of the weight of the inertia masses 7, dependent upon the position of their centres of gravity in relation to pin 19, being transferred through the actuating levers 10 to the single acting cylinder 16.

An inlet 20 for supply of compressed air to the single acting cylinder 16 is located in a block 21 supported at the lower end of a hollow connecting member 22, the upper end of which is connected to the work holder 1.

An inlet 23 for compressed air to effect the up or working stroke of the piston rod 15 of the double acting cylinder '12 and for the exhausting of that part of the cylinder 12 is also located in the block 21 and connection with the cylinder 12 is made through two sets of ports 2.4, 25 in the hollow connecting member 22.

The double acting cylinder 12 floats on the single acting cylinder 16, and is mounted about and slides with respect to the hollow connecting member 22.

An inlet 25 for both supply of compressed air for the down or return stroke of the piston rod 15 and also for exhausting of that part of the cylinder 12 is located in the upper part of the cylinder 12.

Both inlets 23, 26 are controlled by two way valves of conventional design which are not shown.

Because the cylinder 12 moves with respect to the hollow connecting member 22, the lower limit of the travel of the piston on the rod 15 is maintained at a level above the ports 25.

The punches 3 are constrained rotationally of the mandrel axes so that the blades of the punches, corresponding to the root form of the teeth to be formed, are always parallel in a developed plane circumferential of the work blank 2 and at an angle to the axis of the blank corresponding to the helix angle of the gear to be formed.

In operation, a blank 2 heated to the appropriate forging temperature is placed in work holder 1 and located by a Work retainer 27 and clamp 28. A reservoir of compressed air (not shown) is valved to the working area of the double-acting cylinder to produce an up stroke of the piston rod 15 and a downward movement of the cylinder 12, thus forcing apart the pivots 13 and 14 of the actuating levers 1t and links 11, which thereby serve to drive the inertia masses 7 radially inwards over a travel and at such speed, before the punches 3 contact the blank 2, as to impart to the punches suflicient kinetic energy for optimum economic forming. At a suitable point during the travel valving is reversed to direct the air from pressure source to the return or upside of the double-acting cylinder 12 and to vent the working area or downside so that the punches 3 are withdrawn from contact with the hot metal as soon as the kinetic energy of the inertia masses 7 and associated linked masses has dissipated itself in penetrating the periphery of the blank 2.

The geometry of the actuating levers 10 and links 11 in relation to the horizontal planar movement of the inertia masses 7 is such that both the cylinder 12 and piston rod 15 assemblages must move relatively in the vertical. To accommodate this, an air supply at a substantially constant pressure is introduced through the inlet to the single acting cylinder 16 so that the double acting cylinder 12 and ancillary items including a proportion of the weight of the inertia masses 7 are supported counter to the force of gravity regardless of the vertical relationship on the hollow connecting member 22.

In forming some materials it is convenient to punch the full form depth at one blow, but other materials, and in particular certain exotic metal alloys are more economically worked by repetitive partial penetrations, so the air valving is arranged to be manually or automatically repetitive in action.

Repetitive penetration is peculiarly economic for most cold worked materials as. any lubricant introduced to combat the higher punch loading necessary to achieve penetration, will often break down after only a short penetration. Repetitive punching allows the film of lubricant to reform between successive penetrations and so reduce surface deterioration of the punches. A further improvement in cold punch life is often possible if the punch is not withdrawn with the inertia masses, but is left almost in contact with the work allowing only sufficient clearance between punch and partial impression for induction of the requisite oil film.

To achieve the above, one embodiment of the invention permits a degree of movement between the punches and the inertia masses.

An advantageous feature of the invention is that a machine can easily be adapted for forming different sizes and differently toothed gears. Different mandrels and different punches are normally required and of course a different number of driving linkages where fewer or more teeth are required, but the main set up of doubleacting cylinder and so on can be used for a wide variety of gears.

Although this invention is directed particularly to the formation of involute teeth, it is of course adaptable to the formation of cycloidal, helicoid or any form of chain sprocket teeth.

It is to be understood that the invention is not re stricted to thecxact details shown and described but embraces such modifications as come within the ambit of the accompanying claims:

I claim:

1. A method of forming gear teeth upon metal blanks which comprises subjecting the blank to a simultaneous forging operation by a number, equal to the number of teeth to be formed, of inwardly acting radially disposed tooth ended punches attached to inertia masses to which is applied a penetration velocity high enough to induce radial outwards splash of the deformed metal from the tooth roots of the teeth being formed.

2. A method according to claim 1 in which the blank 4 is worked in aheated condition and the punches are Withdrawn immediately at the limit of penetration or of each partial penetration.

3. A method according to claim 1 in which the blank is worked in a cold condition and the punch tips are left substantially in contact with the partial penetration with enough clearance only between the punch tips and the blank for renewal of lubricant film.

4. A machine for forming gear teeth upon metal blanks by a simultaneous forging operation by a number, equal to the number of teeth to be formed, of radially disposed tooth ended punches, which comprises means to support the gear blank, a multiplicity of suitably shaped and radially guided punches, an inertia mass attached to each punch, and means for simultaneously applying to all of the punches and inertia masses a high speed, high momentum inwards movement to impact the rim of the supported blank, with sufficient penetration velocity to induce radial outwards splash of the deformed metal from the tooth roots of the teeth being formed.

5. A machine according to, claim 4 in which the means to support the gear blank comprises a work holder adapted to accept and locate the blank with the axis of the blank in the vertical.

6. A machine according to claim 4 including an annular guide ring with bushed radial holes in which punch mandrels are located and enabled to slide radially.

7. A machine according to claim 6 in which said inertia masses are attached to the outer ends of the punch mandrels.

8. A machine according to claim 7 including a plurality of suspension links to transfer at least a portion ofthe weight of the overhung inertia masses to, and to compensate for vertical tolerances in, a plurality of actuating levers, intermediately lengthwise of each of which is pivoted an actuating link.

9. A machine according to claim 8 including a double acting air cylinder, centred in relation to the work holder,

and having a plurality of tangential pivots radiating from the cylinder for attachment of the actuating levers and a like plurality radiating from the piston rod for attachment of the actuating links.

10. A machine according to claim 9 including a single acting cylinder associated with said double acting cylinder and with the annular guide ring to provide a floating support for the weight of the double-acting cylinder, of the actuating levers and links, and of that part of the inertia masses supportedthrough the action of the suspension links.

References Cited UNITED STATES PATENTS 444,175 1/1891 West 72-402 524,269 8/1894 West 72-402 632,862 9/1899 Arnold 72402 X 1,507,621 9/1924 Perry et a1 72-41 ILLIAM w. DYER, JR., Primary Examiner. 

1. A METHOD OF FORMING GEAR TEETH UPON METAL BLANKS WHICH COMPRISES SUBJECTING THE BLANK TO A SIMULTANEOUS FORGING OPERATION BY A NUMBER, EQUAL TO THE NUMBER OF TEETH TO BE FORMED, OF INWARDLY ACTING RADIALLY DISPOSED TOOTH ENDED PUNCHED ATTACHED TO INERTIA MASSES TO WHICH IS APPLIED A PENETRATION VELOCITY HIGH ENOUGH TO INDUCE RADIAL OUTWARDS SPLASH OF THE DEFORMEDD METAL FROM THE TOOTH ROOTS OF THE TEETH BEING FORMED. 